1. Field of the Invention
The present invention relates to a system of management of assembly line production, for example automobiles assembly line production, in which different models of work objects are sequentially being processed and assembled.
2. Prior Art
In a typical line production, various work stations are disposed along a production line, and the work objects are moved along the line from work station to station. In the respective work station, the various mechanical operations are applied to the work objects which come thereto. In the case of producing automobiles (referred to as cars hereinafter) and the like, a number of different models of cars is processed and assembled through the same production line. For that reason, the operations of respective work stations must be properly controlled so that the appropriate mechanical operations for the models and classes of the work objects are performed by respective work stations.
Conventionally, in order to achieve the production of different models, a series of data conversion processes are performed by operators. Hereinafter, the description will be given with respect to such data conversion processes with reference to FIG. 16.
Work commands are given and stacked on demand in the line production, and work sequence data, in which the respective work commands are organized in the order of work priority sequence, are updated. Each work command includes such information as model types (model year, manufacturing plant, 2- or 4-door) to be produced, family groups (domestic or foreign) and options (sunroof and others), lot number (given to each lot of a group of same type of cars), lot size (the quantity of cars to be produced). Basically, the processing to be applied to the work objects depend on the type of cars such as the models and classes of that. In the first conversion shown in FIG. 16, the work sequence data are rearranged for respective work stations in the line production, whereby step sequence data which define the sequence of processing steps for respective models and classes of cars are obtained and supplied to respective work stations. Next, in the second step, in each work station, an operator sequentially picks up work commands from the step sequence data, and converts the picked up work command into the processing pattern data containing a series of commands to be given to processing machines in that station (the second conversion), after which the operator enters the commands to a controller according to the processing pattern data. In this manner, the work sequence data needed to be correlated twice, manually. In each processing machine, the command manually entered by the operator is converted to the job code which designates the operation to be performed by that processing machine based on a correlation table which is stored in internal memory and contains a set of job codes corresponding to respective commands (the third conversion). The job code contains information on the processing tool bit numbers, fabrication patterns, job numbers for the automated processing machine (for example, action patterns, numbers to represent welding conditions). In this manner, processing pattern data are manually generated and sequentially entered to controller, whereby the work objects are sequentially supplied to the respective processing machine in order of their work priorities and the appropriate operations according to that processing pattern data are applied to the work objects.
For example, in the operation to weld side panels to floor panels, work sequence data are converted into step sequence data which are converted into machine patterns recognizable by the machine, and are entered into the welding controller. The welding machine then takes out appropriate side and floor panels, according to the model and class information specified in the work and step sequence data, and sets the panels into proper jigs and prepares machine codes and welds the two panels according to machine patterns appropriate for the model and class, and thereby accomplishes an assembling operation of side panels to floor panels.
As described above, the conventional procedure of operating the assembly line was labor-intensive since each work station required manual inputting of processing data into each automated processing machine. Accordingly, management of such a system was inefficient, and in spite of line automation, the production efficiency was also low because of the extra work load such a system created. In addition, when there is a change in the production schedule, such as production of another model, the content of the work sequence must be changed correspondingly. Thus, processing data, such as the processing pattern data, need to be changed correspondingly, and for every change, the work station operator needs to be instructed on the change protocol. The same problem arises when there are changes due to customer order or rework, requiring loading of different processing data. Further, processing instruction data contain a large number of identification codes according to their model, work sequence, machine job patterns and many other information codes to correlate various car bodies with their processing requirements. When a change is to be made to such masses of data, the operator was confronted with a difficult manual task of analyzing the data and identifying the necessary corrective actions to be made throughout his own line. Furthermore, such an action in one line would inevitably affect the productivity of not only his own line but other processes and lines as well, resulting in a serious loss of overall productivity of a plant.